Your best change is to use omxplayer since it uses hardware GPU and is fast enough if you get it to work. I am streaming two (640x480@10) mjpeg streams with omxplayer like this: omxplayer --win "0 544 640 1024" --live 'http://192.168.254.212/cgi-bin/nph-zms?monitor=2&maxfps=10&buffer=4000' try if --...

It is possible that there is a fix in new rasbian or firmware which fixes this. Maybe Class 10 SD card is not working with your Raspbian version.
To proove that it would be a good idea to test with new version of Rasbian.

Looking the new 2B+, the power circuits looks different than in B+ and I have learned that it uses a bit more power. Is it now safe to feed for example 6 V to the microUSB or is it still limited to 5V only?